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make slaves of the conquered ants. There are numerous species of the so-called slave-making ants. The slave-makers carry into their own nest the eggs and larvæ and pupe of the conquered community, and when these come to maturity they act as slaves of the victors—that is, they collect food, build additions to the nests, and care for the young of the slavemakers. This specialization goes so far in the case of some kinds of ants, like the robber-ant of South America (Eciton), that all of the Eciton workers have become soldiers, which no longer do any work for themselves. The whole community lives, therefore, wholly by pillage or by making slaves of other kinds of ants. There are four kinds of individuals in a robberant community-winged males, winged females, and small and large wingless soldiers. There are many more of the small soldiers than of the large, and some naturalists believe that the few latter, which are distinguished by heads and jaws of great size, act as officers! On the march the small soldiers are arranged in a long, narrow column, while the large soldiers are scattered along on either side of the column and appear to act as sentinels and directors of the army. The observations made by the European students of ants, Huber, Forel, Emery and Wasmann, and by McCook and Wheeler in America, read like fairy tales, and yet are the well-attested actual phenomena of the extremely specialized communal and social life of these animals.

The bumblebees and social wasps show an intermediate condition between the simply gregarious or neighborly mining bees and the highly developed, permanent honeybee and ant communities. Naturalists believe that the highly organized communal life of the honeybees and the ants is a development from some simple condition like that of the bumblebees and social wasps, which in its turn has grown out of a still simpler, more gregarious assembly of the individuals of one species. It is not difficult to see how such a development could in the course of a long time take place.

The termites or white ants (not true ants) are also communal insects. Some species of termites in Africa live in great mounds of earth, often fifteen feet high. The community comprises hundreds of thousands of individuals, which are of as many as eight kinds or castes (Fig. 247) viz., sexually active winged males, sexually active winged females, other fertile males and females

which are wingless, wingless workers of both sexes not capable of reproduction, and wingless soldiers of both sexes also incapable of reproduction. The production of new individuals is the sole business of the fertile males and females; the workers build the nest and collect food, and the soldiers protect the community from the attacks of marauding insects. The egglaying queen grows to monstrous size in some species, being sometimes four or five inches long, while the other individuals of the community are not more than half or three-quarters of an inch long. The great size of the queen is due to the enormous number of eggs in her body.

We have pointed out elsewhere that the complexity of the bodies of the higher animals depends on a specialization or differentiation of parts, due to the assumption of

Fig. 247.— Termites: a, Queen; b, male; c, worker ; different functions or duties by different parts of the body; that the degree of structural differentiation depends on the degree or extent of division of labor shown in the economy of the animal. It is obvious that the same principle of division of labor with accompanying modification of structure is the basis of colonial and communal life. It is simply a manifestation of the principle among individuals instead of among organs. The division of the necessary labors of life among the different zooids of the colonial jellyfish is plainly the reason for the profound and striking, but always reasonable and explicable, modifications of the typical polyp or medusa body, which is shown by the swimming zooids, the feeding zooids, the sense zooids, and the others of the colony. And similarly in the case of the termite community, the soldier individuals are different structurally from the worker in

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d, soldier.

dividuals because of the different work they have to do. And the queen differs from all the others, because of the extraordinary prolificacy demanded of her to maintain the great community.

It is important to note, however, that among those animals that show the most highly organized or specialized communal or social life, the structural differences among the individuals are the least marked, or at least are not the most profound. The three kinds of honeybee individuals differ but little; indeed, as two of the kinds, male and female, are to be found in the case of almost all kinds of animals, whether communal in habit or not, the only unusual structural specialization in the case of the honeybee, is the presence of the worker individual, which differs from the other individuals primarily in the rudimentary condition of the reproductive glands. Finally, in the case of man, with whom the communal or social habit is so all-important as to gain for him the name of "the social animal,” there is no differentiation of individuals adapted only for certain kinds of work. Among these highest examples of social animals, the presence of an advanced mental endowment, the specialization of the mental power, the power of reason, have taken the place of and made unnecessary the structural differentiation of individuals. The honeybee workers do different kinds of work: some gather food, some care for the young, and some make wax and build cells, but the individuals are interchangeable; each one knows enough to do these various things. There is a structural differentiation in the matter of only one special work or function, that of reproduction.

With the ants there is, in some cases, a considerable structural divergence among individuals, as in the genus Atta of South America with six kinds of individuals—namely, winged males, winged females, wingless soldiers, and wingless workers of three distinct sizes. In the case of other kinds with quite as highly organized a communal life, there are but three kinds of individuals; the winged males and females and the wingless workers. The workers gather food, build the nest, guard the “cattle” (aphids), make war, and care for the young. Each one knows enough to do all these various distinct things. Its body is not so modified that it is limited to doing but one kind of thing.

The increase of intelligence, the development of the power of reasoning, is the most potent factor in the development of a highly specialized social life. Man is the example of the highest development of this sort in the animal kingdom, but the highest form of social development is not by any means the most perfectly communal.

The advantages of communal or social life, of coöperation and mutual aid, are real. The animals that have adopted such a life are among the most successful of all animals in the struggle for existence. The termite individual is one of the most defenseless, and, for those animals that prey on insects, one of the most toothsome luxuries to be found in the insect world. But the termite is one of the most abundant and

widespread and successfully living insect kinds in all the tropics. .

Where ants are not, few insects are. The honeybee is a popular type of a successful life. The artificial protection afforded the honeybee by man may aid in its struggle for existence, but it gains this protection because of certain features of its communal life, and in Nature the honeybee takes care of itself well. The Little Bee People of Kipling's Jungle Book, who live in great communities in the rocks of Indian hills, can put to rout the largest and fiercest of the jungle animals. Cooperation and mutual aid are among the most important factors which help in the struggle for existence. Its great advantages are, however, in some degree balanced by the fact that mutual help brings mutual dependence. The community or society can accomplish greater things than the solitary individuals, but coöperation limits freedom, and often sacrifices the individual to the whole.

CHAPTER XIX

COLOR AND PATTERN IN ANIMALS

In spite of the fluency with which so many people talk of the meaning of color in organisms, the subject is as incomplete on the theoretical as on the physiological side. ... The two deficiencies are related and a little more physiology will arm the theorists with better weapons.-NEWBIGIN.

A CONSPICUOUS characteristic of the animal body is its color pattern. Not all kinds of animals attract our attention by their colors: there are even whole groups whose uniform monochrome color scheme is of a sort to relieve them completely from any imputation of flaunting showiness or of bizarre fancies in personal decoration. But consider such a class as the insects: the painted butterflies, the burnished beetles, the flashing dragon flies, the green katydids and brown locusts. All attract attention first by the variety or intensity of their colors and the arrangement of these colors in simple or intricate symmetry of pattern. Even the small and at casual glance, obscure and monochrome insects often reveal, on careful examination, a large degree of color development and ofttimes amazing intricacy and beauty of pattern. So uniformly developed is color pattern among insects, that no thoughtful collector or observer of these animals escapes the self-put question: Why is there such a high degree of specialization of color throughout the insect class? If he be an observer who has taken seriously the teachings of Darwin and the utilitarian school of naturalists, his question becomes couched in this form: What is the use to the insects of all this color and pattern?

For the attitude of any modern student of Nature, confronted by such a phenomenon, is that of the seeker for the significance of the phenomenon. And the key to significance

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